Observations on Maddening, 
I shall here repeat, that for common and low-priced 
articles it is indispensably necessary to employ gall-nuts 
or shumac, which will save one half and even two thirds 
of the madder ; but the colours obtained are neither so 
fixed nor so bright. The addition of chalk, however, 
must not be omitted ; otherwise the gallic acid will carry 
away a portion of the alumine and coloured oxide of 
iron, which will weaken the shades, add, by tarnishing 
the stuffs, will also attack the white which may have 
been preserved in them. Without the addition of gall- 
nuts or shumac, it seemed to me impossible to exhaust 
the madder entirely of its colouring parts ; which made 
me presume that their adhesion is favoured by the viscid 
nature of the tanning principle of these astringent sub- 
stances, which carry away and combine with themselves 
the colouring parts. I shall observe also, that gall-nuts 
as well as shumac lose the property of dyeing black ; 
and acquire, on the other hand, that of dyeing or colour- 
ing alumipe yellow, oxide of iron olive green, by the ad- 
dition of chalk, the calcareous base of which unites it- 
self to the gallic acid. Bo these yellow and olive -green 
colours arise from any peculiar substance contained in 
the gall-nuts and shumac, or are they indebted for their 
origin to the tanning principle ? This remains to be ex- 
amined. 
The quantity of madder to be employed in dyeing 
ought not only to be proportioned to the extent of the 
surfaces to be madder ed, but also to the concentration of 
the liquors of the acetite of alumine and iron, improper- 
ly called mordants ; that is to say, to the greater or less 
quantity of alumine and oxide of iron which these saline 
liquors, either insulated or mixed together, when, they dry 
on the articles to be dyed, may have left or deposited 
there by the evaporation of the acetic acid. If the ofo- 
jects to foe dyed are not numerous, and, in particular, 
